Surface-treated steel sheet for battery containers

ABSTRACT

A surface-treated steel sheet for a battery container, including a steel sheet, an iron-nickel diffusion layer formed on the steel sheet, and a nickel layer formed on the iron-nickel diffusion layer and constituting the outermost layer, wherein when the Fe intensity and the Ni intensity are continuously measured from the surface of the surface-treated steel sheet for a battery container along the depth direction with a high frequency glow discharge optical emission spectrometric analyzer, the thickness of the iron-nickel diffusion layer being the difference between the depth at which the Fe intensity exhibits a first predetermined value and the depth at which the Ni intensity exhibits a second predetermined value is 0.04 to 0.31 μm; and the total amount of the nickel contained in the iron-nickel diffusion layer and the nickel contained in the nickel layer is 10.8 to 26.7 g/m 2 .

TECHNICAL FIELD

The present invention relates to a surface-treated steel sheet for abattery container.

BACKGROUND ART

Recently, portable devices such as audio instruments and cellular phoneshave been used in various fields, and there have been used as theoperating power sources thereof many primary batteries such as alkalinebatteries and many secondary batteries such as nickel-hydrogen batteriesand lithium-ion batteries. Such batteries are demanded to achieve longoperating lives, high performances and the like by the achievement ofhigh performances of the devices being mounted with such batteries, andthe battery containers packed with power generation elements composed ofpositive electrode active materials, negative electrode active materialsand the like are also demanded to be improved in the performances as theimportant constituent elements of the batteries.

As the surface-treated steel sheets to form such battery containers, forexample, Patent Documents 1 and 2 disclose surface-treated steel sheetseach prepared by forming a nickel plating layer an a steel sheet, andthen forming an iron-nickel diffusion layer by applying a heat treatmentto the nickel plated steel sheet.

On the other hand, battery containers having a thin battery containerwall (hereinafter, referred to as “can wall”) have been demanded inorder to improve the volume percentage, under the requirements for theachievement of higher capacities and lighter weights of batteries. Forexample, as disclosed in Patent Documents 3 and 4, it has been known aprocessing allowing the thickness of the can wall after the processingto be thinner than the thickness of a surface-treated steel sheet beforethe processing.

RELATED ART Patent Documents

-   Patent Document 1: Japanese Patent Laid-Open No. 2014-009401-   Patent Document 2: Japanese Patent Laid-Open No. 6-2104-   Patent Document 3: International Publication No. WO 2009/107318-   Patent Document 4: International Publication No. WO 2014/156002

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, in Patent Documents 1 and 2, the heat treatment condition inthe formation of the iron-nickel diffusion layer is a high temperatureor a long time, and the inter-diffusion between the iron in the steelsheet serving as a substrate and the nickel in the nickel plating layertends to proceed in the resulting surface-treated steel sheet. Thepresent inventors have obtained a finding that when a heat treatment isperformed under the conventional heat treatment conditions, use of abattery with the surface treated steel sheet processed into a batterycontainer sometimes increases the amount of iron dissolved from theinner surface of the battery container, and the corrosion resistance isliable to be decreased. The iron exposed during formation of the batterycontainer is favorable for improving the battery properties; however astudy performed by the present inventors have revealed that whenthickness of the nickel plating layer formed before heat treatment isthin, the exposure of the iron is locally increased. With increaseddissolution amount, the corrosion resistance is liable to be decreased.

In addition, in Patent Documents 3 and 4, there is a problem that byreducing the thickness of the can wall of the battery container, theamount of iron dissolved an the inner surface of the battery containersometimes comes to be increased, and the corrosion resistance of theinner surface of the battery container is decreased.

An object of the present invention is to provide a surface-treated steelsheet for a battery container excellent in corrosion resistance evenwhen the volume percentage is improved by reducing the thickness of thecan wall in the case where the surface-treated steel sheet is processedinto a battery container.

Means for Solving the Problem

According to the present invention, there is provided a surface-treatedsteel sheet for a battery container, including a steel sheet, aniron-nickel diffusion layer formed an the steel sheet, and a nickellayer formed on the iron-nickel diffusion layer and constituting theoutermost surface layer, wherein when the Fe intensity and the Niintensity are continuously measured along the depth direction from thesurface of the surface-treated steel sheet for a battery container, byusing a high frequency glow discharge optical emission spectrometricanalyzer, the thickness of the iron-nickel diffusion layer, being thedifference (D2−D1) between the depth (D1) at which the Fe intensityexhibits a first predetermined value and the depth (D2) at which the Niintensity exhibits a second predetermined value, is 0.04 to 0.31 μm, andthe total amount of nickel contained in the iron-nickel diffusion layerand the nickel layer is 10.8 to 26.7 g/m².

It is to be noted that the depth (D1) exhibiting the first predeterminedvalue is the depth exhibiting an intensity of 10% of the saturated valueof the Fe intensity measured by the above-described measurement, and thedepth (D2) exhibiting the second predetermined value is the depthexhibiting an intensity of 10% of the maximum value when the measurementis further performed along the depth direction after the Ni intensityshows the maximum value by the above-described measurement.

In the surface-treated steel sheet for a battery container of thepresent invention, the ratio of the thickness of the iron-nickeldiffusion layer to the thickness of the nickel layer (thickness ofiron-nickel diffusion layer/thickness of nickel layer) is preferably0.013 to 0.5.

In the surface-treated steel sheet for a battery container of thepresent invention, the thickness of the nickel layer is preferably 1.0μm or more.

In the surface-treated steel sheet for a battery container of thepresent invention, the Vickers hardness (HV) of the nickel layermeasured with a load of 10 gf is preferably 220 to 280.

According to the present invention, there is provided a batterycontainer made of the above-described surface-treated steel sheet for abattery container.

According to the present invention, there is also provided a batteryprovided with the above-described battery container.

Moreover, according to the present invention, there is provided a methodfor producing a surface-treated steel sheet for a battery container,including: a nickel plating step of forming a nickel plating layer witha nickel amount of 10.8 to 26.7 g/m²; and a heat treatment step ofapplying a heat treatment to the steel sheet having the nickel platinglayer formed thereon by maintaining the steel sheet at a temperature of450 to 600° C. for 30 seconds to 2 minutes.

Effects of Invention

According to the present invention, it is possible to provide asurface-treated steel sheet for a battery container excellent incorrosion resistance even when the volume percentage is improved byreducing the thickness of the can wall when a battery container is madeof the surface-treated steel sheet for a battery container. Moreover,according to the present invention, it is possible to provide a batterycontainer and a battery obtained by using such a surface-treated steelsheet for a battery container.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an oblique perspective view showing one embodiment of abattery undergoing an application of the surface-treated steel sheet fora battery container according to the present invention.

FIG. 2 is a cross-sectional view along the line II-II in FIG. 1.

FIG. 3 is an enlarged cross-sectional view of the portion III in FIG. 2,in one embodiment of the surface-treated steel sheet for a batterycontainer of the present invention.

FIG. 4 is a diagram for illustrating the method for producing thesurface-treated steel sheet for a battery container shown in FIG. 3.

FIG. 5 presents the graphs for illustrating the method for measuring thethickness of an iron-nickel diffusion layer.

FIG. 6 presents a photograph for illustrating the method for measuringthe average crystal grain size in the surface portion of a nickel layer.

DESCRIPTION OF EMBODIMENTS

Hereinafter, one Embodiment of the present invention is described by wayof the accompanying drawings. The surface-treated steel sheet for abattery container according to the present invention is processed intoan external shape corresponding to the desired shape of a battery.Examples of a battery may include, without being particularly limitedto: primary batteries such as an alkaline battery, and secondarybatteries such as a nickel-hydrogen battery and a lithium-ion battery;as the members of the battery containers of these batteries, thesurface-treated steel sheet for a battery container according to thepresent invention can be used. Hereinafter, the present invention isdescribed on the basis of an embodiment using the surface-treated steelsheet for a battery container according to the present invention for apositive electrode can constituting the battery container of an alkalinebattery.

FIG. 1 is an oblique perspective view showing one embodiment of analkaline battery 2 undergoing an application of the surface-treatedsteel sheet for a battery container according to the present invention,and FIG. 2 is a cross-sectional view along the line II-II in FIG. 1. Thealkaline battery 2 of the present example includes a positive electrodemixture 23 and a negative electrode mixture 24 filled inside thepositive electrode can 21 having a bottomed cylindrical shape throughthe intermediary of a separator 25; and a sealing body constituted witha negative electrode terminal 22, a current collector 26 and a gasket 27caulked an the inner surface side of the opening section of the positiveelectrode can 21. A convex positive electrode terminal 211 is formed inthe bottom center of the positive electrode can 21. In addition, anexterior case 29 is mounted on the positive electrode can 21 through theintermediary of an insulating ring 28, for the purpose of impartinginsulation properties, improving the design, and the like.

The positive electrode can 21 of the alkaline battery 2 shown in FIG. 1is obtained by mold-processing the surface-treated steel sheet for abattery container according to the present invention, by applying, forexample, a deep drawing processing method, a drawing and ironingprocessing method (DI processing method), a drawing thin and redrawingprocessing method (DTR processing method), or a processing method usinga stretch processing and an ironing processing after a drawingprocessing. Hereinafter, with reference to FIG. 3, the constitution ofthe surface-treated steel sheet for a battery container (surface-treatedsteel sheet 1) according to the present invention is described.

FIG. 3 is an enlarged cross-sectional view of the portion III of thepositive electrode can 21 shown in FIG. 2, and the upper side in FIG. 3corresponds to the inner surface (the surface in contact with thepositive electrode mixture 23 of the alkaline battery 2) of the alkalinebattery 2 of FIG. 1. The surface-treated steel sheet 1 of the presentembodiment includes, as shown in FIG. 3, an iron-nickel diffusion layer12 and a nickel layer 14 formed on a steel sheet 11 constituting thesubstrate of the surface-treated steel sheet 1.

In the surface-treated steel sheet 1 of the present embodiment, thethickness of the iron-nickel diffusion layer 12 measured by a highfrequency glow discharge optical emission spectrometric analyzer is 0.04to 0.31 μm, and the total amount of the nickel contained in theiron-nickel diffusion layer 12 and the nickel layer 14 is 10.8 to 26.7g/m². Herewith, the surface-treated steel sheet 1 of the presentembodiment is excellent in corrosion resistance even in the case wherethe thickness of the can wall is reduced to improve the volumepercentage when the surface-treated steel sheet 1 is processed into abattery container.

<Steel Sheet 11>

The steel sheet 11 of the present embodiment is not particularly limitedas long as the steel sheet 11 is excellent in molding processability;for example, a low carbon aluminum-killed steel (carbon content: 0.01 to0.15% by weight), a low carbon steel having a carbon content of 0.003%by weight or less, or a non-aging low carbon steel prepared by addingTi, Nb or the like to a low carbon steel can be used. The thickness ofthe steel sheet is not particularly limited, but is preferably 0.2 to0.5 nm. When the steel sheet is too thick, the heat quantity necessaryfor diffusion is deficient, and the diffusion layer is liable to beformed insufficiently. When the steel sheet is too thin, the thicknessnecessary as the subsequent battery sometimes cannot be secured, or theheat conduction is fast and the control of the thickness of thediffusion layer is liable to be difficult.

In the present embodiment, the hot rolled sheets of these steels arewashed with an acid to remove the scales (oxide film), then cold rolled,then electrolytically washed, then annealed and subjected to temperrolling, and are used as the steel sheets 11; or alternatively, the hotrolled sheets of these steels washed with an acid to remove the scales(oxide film), then cold rolled, then electrolytically washed, thensubjected to temper rolling without being subjected to annealing, andare used as the steel sheets 11.

<Iron-Nickel Diffusion Layer 12, and Nickel Layer 14>

In the surface-treated steel sheet 1 of the present embodiment, theiron-nickel diffusion layer 12 is a layer allowing iron and nickel tomutually diffuse therein, formed as a result of a thermal diffusiontreatment performed after the nickel plating layer 13 is formed on thesteel sheet 11, so as to cause the thermal diffusion of the ironconstituting the steel sheet 11 and the nickel constituting the nickelplating layer 13. The nickel layer 14 is a layer derived from theportion free from the diffusion of iron in the vicinity of the surfacelayer of the nickel plating layer 13, the portion being thermallyrecrystallized and softened when the thermal diffusion treatment isperformed.

By forming the iron-nickel diffusion layer 12 obtained by such a thermaldiffusion treatment, when the surface-treated steel sheet 1 is used as abattery container, the direct, wide area contact of the steel sheet withthe electrolytic solution or the like constituting the battery can beprevented; and moreover, the presence of the iron-nickel diffusion layer12 relaxing the potential difference between the nickel of the nickellayer 14 and the iron of the steel sheet 11 allows the corrosionresistance and the battery properties to be satisfactory. The formationof the iron-nickel diffusion layer 12 also allows the adhesivenessbetween the steel sheet 11 and the nickel layer 14 to be improved.

The nickel plating layer 13 for forming the iron-nickel diffusion layer12 can be formed on the steel sheet 11 by using, for example, a nickelplating bath. As the nickel plating bath, there can be used a platingbath usually used in nickel plating, namely, a Watts bath, a sulfamatebath, a boron fluoride bath, a chloride bath and the like. For example,the nickel plating layer 13 can be formed by using, as a watts bath, abath having a bath composition containing nickel sulfate in aconcentration of 200 to 350 g/L, nickel chloride in a concentration of20 to 60 g/L, and boric acid in a concentration of 10 to 50 g/L, underthe conditions that the pH is 3.0 to 4.8 (preferably pH is 3.6 to 4.6),the bath temperature is 50 to 70° C., the current density is 10 to 40A/dm² (preferably 20 to 30 A/dm²).

It is to be noted that as the nickel plating layer 13, asulfur-containing bright plating is not preferable because the batteryproperties are liable to be degraded; however, it is possible in thepresent invention to apply a matte plating not containing sulfur in anamount equal to or more than the amount of an inevitable impurity aswell as a semi-gloss plating. This is because the hardness of the layerobtained by plating is as follows: the semi-gloss plating is harder thanthe matte plating, but the heat treatment for forming the diffusionlayer in the present invention allows the hardness of the semi-glossplating to be comparable with or slightly higher than the hardness ofthe matte plating. When a semi-gloss plating is formed as a nickelplating layer, a semi-gloss agent may be added to the above-describedplating baths. The semi-gloss agent is not particularly limited as longas the semi-gloss agent allows the nickel plating layer after plating tobe free from sulfur (for example, 0.05% or less in an fluorescent X-raymeasurement); as the semi-glass agent, it is possible to use, forexample, an aliphatic unsaturated alcohol such as a polyoxyethyleneadduct of an unsaturated alcohol, an unsaturated carboxylic acid,formaldehyde, and coumarin.

In the present embodiment, as shown in FIG. 4, the above-describednickel plating layer 13 is formed on the steel sheet 11, andsubsequently a thermal diffusion treatment is performed; thus, theiron-nickel diffusion layer 12 and the nickel layer 14 are formed, andthe surface-treated steel sheet 1 as shown in FIG. 3 can be obtained.

In the present embodiment, the nickel amount in the nickel plating layer13 before performing the thermal diffusion treatment corresponds to thetotal amount of the nickel contained in the iron-nickel diffusion layer12 and the nickel contained in the nickel layer 14 obtained by thethermal diffusion treatment.

The total amount (the nickel amount in the nickel plating layer 13before performing the thermal diffusion treatment) of the nickelcontained in the iron-nickel diffusion layer 12 and the nickel containedin the nickel layer 14 obtained by the thermal diffusion treatment maybe 10.8 to 26.7 g/m, is preferably 13.3 to 26.7 g/n, and is morepreferably 17.8 to 25.8 g/m². When the total amount of the nickelcontained in the iron-nickel diffusion layer 12 and the nickel containedin the nickel layer 14 is too small, the improvement effect of thecorrosion resistance due to nickel is insufficient, and the corrosionresistance of the obtained surface-treated steel sheet 1 used as abattery container is degraded. On the other hand, when the total amountof the nickel contained in the iron-nickel diffusion layer 12 and thenickel contained in the nickel layer 14 is too large, the can wallthickness of the battery container made of the obtained surface-treatedsteel sheet 1 comes to be thick and the volume of the interior of thebattery container comes to be small (the volume percentage is degraded).In addition, in the case where in the formation of a battery container,a processing is performed in such a way that the can wall thickness at aposition of 5 nm from the bottom of the battery can is reduced by 10% ormore in relation to the sheet thickness of the surface-treated steelsheet 1, when the total amount of nickel is large, a nickel powder tendsto be generated during pressing. When a large amount of the nickelpowder attaches to the punch, there is caused a problem that the nickelpowder attaches to the inner surface of the formed battery container.The total amount of the nickel contained in the iron-nickel diffusionlayer 12 and the nickel contained in the nickel layer 14 can bedetermined by a method calculating on the basis of the total amount(total weight) of the nickel contained in the iron-nickel diffusionlayer 12 and the nickel contained in the nickel layer 14 measurable withan ICP analysis method. Alternatively, the total amount of the nickelcontained in the iron-nickel diffusion layer 12 and the nickel containedin the nickel layer 14, can also be determined by a method calculatingon the basis of the measured deposition amount obtained by measuring thedeposition amount of the nickel atoms constituting the nickel platinglayer 13 by performing a fluorescent X-ray measurement after theformation of the nickel plating layer 13 and before performing thethermal diffusion treatment.

The conditions of the thermal diffusion treatment may be appropriatelyselected according to the thickness of the nickel plating layer 13; theheat treatment temperature is preferably 450 to 600° C., more preferably480 to 590° C., and further preferably 500 to 550° C.; the soaking timein the heat treatment is preferably 30 seconds to 2 minutes, morepreferably 30 to 100 seconds, and further preferably 45 to 90 seconds.In addition, in the heat treatment, the time including the heating uptime and the cooling time in addition to the soaking time is preferably2 to 7 minutes and more preferably 3 to 5 minutes. The thermal diffusiontreatment method is preferably a continuous annealing method from theviewpoint of easy regulation of the heat treatment temperature and theheat treatment time within the above-described ranges.

In the present invention, as described above, by performing the thermaldiffusion treatment, the iron-nickel diffusion layer 12 can be formedbetween the steel sheet 11 and the nickel layer 14, and consequently thesurface-treated steel sheet 1 is allowed to have a constitution(Ni/Fe-Ni/Fe) having the iron-nickel diffusion layer 12 and the nickellayer 14 on the steel sheet 11 in order from bottom to top.

In the present embodiment, the thickness of the thus formed iron-nickeldiffusion layer 12 measured with a high frequency glow discharge opticalemission spectrometric analyzer may be 0.04 to 0.31 μm, and ispreferably 0.05 to 0.27 μm, more preferably 0.08 to 0.25 μm, and furtherpreferably 0.09 to 0.20 μm. When the thickness of the iron-nickeldiffusion layer 12 is too thin, in the obtained surface-treated steelsheet 1, the adhesiveness of the nickel layer 14 is decreased, andmoreover, when the surface-treated steel sheet 1 is processed into abattery container, the corrosion resistance is decreased. On the otherhand, when the thickness of the iron-nickel diffusion layer 12 is toolarge, the amount of exposed iron comes to be too large in the nickellayer 14 of the surface-treated steel sheet 1, and consequently, whenthe surface-treated steel sheet 1 is used as the battery container, theamount of iron dissolved from the inner surface of the battery containeris large and the corrosion resistance is degraded.

It is to be noted that the thickness of the iron-nickel diffusion layer12 can be determined by continuously measuring the variations of the Feintensity and the Ni intensity in the depth direction from the outermostsurface toward the steel sheet 11 with respect to the surface-treatedsteel sheet 1 by using a high frequency glow discharge optical emissionspectrometric analyzer.

Specifically, first, by using the high frequency glow discharge opticalemission spectrometric analyzer, the Fe intensity in the surface-treatedsteel sheet 1 is measured until the Fe intensity is saturated, and byadopting the saturated value of the Fe intensity as a reference, thedepth giving the Fe intensity 10% of the saturated value is defined asthe boundary between the nickel layer 14 and the iron-nickel diffusionlayer 12. For example, the measurement of the thickness of theiron-nickel diffusion layer 12 is described with reference to FIG. 5(A)showing an example of the results obtained by measuring an actuallyprepared surface-treated steel sheet 1 with a high frequency glowdischarge optical emission spectrometric analyzer. It is to be notedthat, in FIG. 5(A), the ordinate represents the Fe intensity and the Niintensity, and the abscissa represents the measurement time when themeasurement is performed in the depth direction from the surface of thesurface-treated steel sheet 1 by using a high frequency glow dischargeoptical emission spectrometric analyzer.

In the present embodiment, first, the saturated value of the Feintensity is determined on the basis of the measurement results of theFe intensity. The saturated value of the Fe intensity is determined fromthe time variation rate (Fe intensity variation/second) of the Feintensity. The time variation rate of the Fe intensity comes to besteeply large when Fe is detected after the start of the measurement,and decreases after passing the maximum value and is stabilized in thevicinity of approximately zero. The value when the time variation rateis stabilized at approximately zero is the saturated value, andspecifically, when the time variation rate of the Fe intensity canes tobe 0.02 (Fe intensity variation/second) or less, the measurement time inthe depth direction can be taken as the measurement time of thesaturation of the Fe intensity.

In the example shown in FIG. 5(A), the saturated value of the Feintensity is a value of approximately 70 in the vicinity of themeasurement time of 20 seconds, and the depth giving an Fe intensity ofapproximately 7, 10% of the saturated value, can be detected as theboundary between the nickel layer 14 and the iron-nickel diffusion layer12.

On the other hand, the boundary between the iron-nickel diffusion layer12 and the steel sheet 11 can be detected as follows. Specifically, whenthe Ni intensity of the surface-treated steel sheet 1 is measured byusing a high frequency glow discharge optical emission spectrometricanalyzer, the maximum value is extracted from the obtained graph showingthe variation of the Ni intensity, and the depth giving a Ni intensityof 10% of the maximum value after the maximum value has been shown isdetermined as the boundary between the iron-nickel diffusion layer 12and the steel sheet 11. For example, when FIG. 5(A) is referred to, themaximum value of the Ni intensity is approximately 70 in the vicinity ofthe measurement time of 9 seconds, and accordingly the depth giving theNi intensity 10% of the maximum value of the Ni intensity, namely,approximately 7, can be detected as the boundary between the iron-nickeldiffusion layer 12 and the steel sheet 11.

In addition, in the present embodiment, on the basis of the boundariesbetween the layers determined as described above, it is possible todetermine the thickness of the iron-nickel diffusion layer 12.Specifically, when the measurement is performed by using a highfrequency glow discharge optical emission spectrometric analyzer, thetime giving an Fe intensity of 10% of the saturated value of the Feintensity is set as the starting point, the measurement time until thetime giving a Ni intensity of 10% of the maximum value after the Niintensity has exhibited the maximum value is calculated, and on thebasis of the calculated measurement time, the thickness of theiron-nickel diffusion layer 12 can be determined.

In the present invention, as described above, for the nickel-platedsteel sheet having a known plating thickness and having undergone noheat treatment, a high frequency glow discharge optical emissionspectrometric analysis is performed, the thickness calculated as aniron-nickel diffusion layer is taken as the “reference thickness,” andthe difference (D2−D1) between D1 and D2 indicates the value obtained bysubtracting the reference thickness.

It is to be noted that in the measurement with a high frequency glowdischarge optical emission spectrometric analyzer, with the increase ofthe thickness of the nickel plating layer, the reference thicknesscalculated from the measurement of the nickel plating layer comes to beincreased; thus, when the thickness of the iron-nickel diffusion layeris determined, the reference thickness is checked in the platingdeposition amount of each of the layers, or alternatively, it isdesirable that the measurement of the reference thickness is performedin each of the two or more samples, different from each other in theplating deposition amount before performing heat treatment, the relationformula between the plating deposition amount and the referencethickness is determined, and then the thickness of the iron-nickeldiffusion layer is calculated.

It is to be noted that for the purpose of determining the thickness ofthe iron-nickel diffusion layer 12 of the surface-treated steel sheet 1on the basis of the measurement time, the high frequency glow dischargeoptical emission spectrometric analysis, as shown in FIG. 5(B), of thenickel-plated steel sheet having a known plating thickness and havingundergone no thermal diffusion treatment is performed, the thicknesscalculated as the iron-nickel diffusion layer in FIG. 5(B) iscalculated, and the calculated thickness is required to be subtracted atthe time of calculation of the iron-nickel diffusion layer 12 of thesurface-treated steel sheet 1 as the actual measurement object.Specifically, from the thickness of the iron-nickel diffusion layer 12portion (the thickness value obtained in FIG. 5(A) as follows: the timegiving the Fe intensity of 10% of the saturated value of the Feintensity is taken as the starting point, the measurement time until thetime giving the Ni intensity an intensity of 10% of the maximum value ofthe Ni intensity after the Ni intensity has exhibited the maximum valuethereof is converted into the thickness) calculated from the graph ofFIG. 5(A), the thickness calculated in the same manner from the graph ofFIG. 5(B) is subtracted, and thus, the thickness of the actualiron-nickel diffusion layer 12 in the graph of FIG. 5(A) can bedetermined.

In addition, by measuring the nickel-plated steel sheet having undergoneno thermal diffusion treatment, the relation between the depth time (themeasurement time based on the high frequency glow discharge opticalemission spectrometric analyzer) and the actual thickness can bedetermined, and accordingly, by using this relation (the relationshowing the relation between the depth time and the actual thickness),the depth time can be converted into the thickness of the iron-nickeldiffusion layer 12 of the surface-treated steel sheet 1 to be the actualmeasurement object.

It is to be noted that when the thickness of the iron-nickel diffusionlayer 12 is measured as described above with a high frequency glowdischarge optical emission spectrometric analyzer, sometimes there is adetection limit value of the thickness of the iron-nickel diffusionlayer 12, due to the performances of the high frequency glow dischargeoptical emission spectrometric analyzer, the measurement conditions orthe like. For example, when a heat-treated nickel-plated steel sheet 1prepared by using, as the steel sheet 11, a steel sheet having a surfaceroughness Ra of 0.05 to 3 μm, as measured with a stylus-type roughnessmeter, is measured with a measurement diameter of ϕ5 mm of a highfrequency glow discharge optical emission spectrometric analyzer, thedetectable region (detection limit value with respect to shape) isapproximately 0.04 μm; when the thickness of the iron-nickel diffusionlayer 12 measured with the high frequency glow discharge opticalemission spectrometric analyzer is equal to or less than the detectionlimit value, the thickness of the iron-nickel diffusion layer 12 can beregarded to be more than 0 μm and less than 0.04 μm. In other words, inthe case where the nickel plating layer 13 is formed on the steel sheet11, and subsequently the iron-nickel diffusion layer 12 and the nickellayer 14 are formed by performing a thermal diffusion treatment, evenwhen the thickness of the iron-nickel diffusion layer 12 is equal to orless than the detection limit value in the measurement of the thicknessof the iron-nickel diffusion layer 12 by using the high frequency glowdischarge optical emission spectrometric analyzer, the thickness of theiron-nickel diffusion layer 12 can be regarded to be more than 0 μm andless than 0.04 μm. It is to be noted that when the nickel plating layer13 is formed on the steel sheet 11, and then a nickel-plated steel sheetis obtained by applying no thermal diffusion treatment, the iron-nickeldiffusion layer 12 can be regarded not to be formed in the nickel-platedsteel sheet (the thickness of the iron-nickel diffusion layer 12 is 0).

The thickness of the iron-nickel diffusion layer 12 is increased withthe increase of the heat treatment temperature, or with the increase ofthe heat treatment time which allows the mutual diffusion of iron andnickel to proceed easily. Because iron and nickel mutually diffuse, theformed iron-nickel diffusion layer 12 extends on the side of the steelsheet 11 and also diffuses on the side of the nickel plating layer 13,in relation to the interface between the steel sheet 11 and the nickelplating layer 13 before the diffusion. When the heat treatmenttemperature is set to be too high, or the heat treatment time is set tobe too long, the iron-nickel diffusion layer 12 comes to be thick, andthe nickel layer 14 canes to be thin. For example, the thickness of theiron-nickel diffusion layer 12 comes to be more than 0.31 μm. Thepresent inventors have discovered that when such a surface-treated steelsheet 1 is molded into a battery container, there occurs an increase ofthe dissolution amount probably caused by the increase of the exposureof iron. The causes for the exposure of iron on the inner surface of thebattery container are probably the exposure of a large amount of iron onthe inner surface of the battery container and the appearance of localiron exposure portions, not only in the case where the thickness of thenickel layer 14 nearly vanishes and iron reaches the surface layer inthe surface-treated steel sheet 1, but also in the case where iron doesnot reach the surface layer in the state of the surface-treated steelsheet 1. In this case, when the surface-treated steel sheet 1 is storedor used as a battery container over a long term, there is an adversepossibility that iron is dissolved from the local iron exposure portionsinto the electrolytic solution, and the gas generated due to thedissolution of iron increases the internal pressure of the interior ofthe battery.

In particular, the present inventors have discovered that the corrosionresistance is liable to be more decreased, in the case where the nickelplating layer is made thin for the purpose of achieving a high batterycapacity, or in the case where a processing is performed to make thethickness of the can wall after forming a battery can thinner than thethickness of the surface-treated steel sheet before forming the batterycan for the purpose of achieving a high battery capacity, because theprocessing conditions for the surface-treated steel sheet 1 are moresevere as compared with the processing allowing the thickness of the canwall to be approximately the same as the thickness of thesurface-treated steel sheet before the formation of the battery can; thepresent inventors have revealed that the surface-treated steel sheet 1of the present embodiment exhibits a marked corrosion resistance evenunder such severe processing conditions. Moreover, for the purpose ofachieving a high battery capacity, it is possible to make thin thethickness of the nickel plating layer and to make thin the thickness ofthe can wall; however, either of these approaches offers a factor todegrade the corrosion resistance of the battery container. The presentinventors have found a new problem of the compatibility of theseapproaches for achieving a high capacity and the corrosion resistanceimprovement with respect to the conventional surface-treated steelsheets, and have found a new constitution capable of coping with theachievement of a high capacity.

It is to be noted that when the thickness of the iron-nickel diffusionlayer 12 is made too thin, the formation of the iron-nickel diffusionlayer 12 comes to be insufficient, and as described above, when thesurface-treated steel sheet 1 is used as a battery container, thecorrosion resistance improvement effect due to the iron-nickel diffusionlayer 12 and the improvement effect of the adhesiveness of the nickellayer 14 due to the iron-nickel diffusion layer 12 are not sufficientlyobtained. In particular, the present inventors have revealed that in thecase where a processing for making thin the thickness of the can wall isapplied for the purpose of achieving a high capacity, the corrosionresistance improvement effect is not obtained when the thickness of theiron-nickel diffusion layer is too thin, even in the presence of thethickness of the nickel layer 14 as the upper layer; however, a markedeffect is obtained when there is formed an iron-nickel diffusion layer12 having a thickness of 0.04 μm or more, detectable by the highfrequency glow discharge optical emission spectrometric analyzer (GDS).

In the present embodiment, as described above, with respect to thesurface-treated steel sheet 1, by setting the thickness of theiron-nickel diffusion layer 12 to be comparatively as thin as 0.04 to0.31 μm, and by controlling the total amount of the nickel contained inthe iron-nickel diffusion layer and the nickel contained in the nickellayer so as to fall within a range from 10.8 to 26.7 g/m², it ispossible to provide a surface-treated steel sheet 1 excellent incorrosion resistance even when the volume percentage is improved bymaking thin the thickness of the can wall when the surface-treated steelsheet 1 is processed into a battery container. It is to be noted thatwhen thickness of the can wall of a battery container is made thin, theamount of iron dissolved on the inner surface of the battery containersometimes has hitherto come to be large, and consequently the corrosionresistance of the inner surface of the battery container is sometimesdegraded. On the other hand, as a method for improving the corrosionresistance when formed into a battery container, there is a method tomake thick the thickness of the iron-nickel diffusion layer and thethickness of the nickel layer formed on the inner surface of the batterycontainer; however, in this case, there is a problem that the thicknessof the can wall comes to be thick when formed into a battery container,and consequently the volume percentage is degraded. Accordingly, in thetechnique for the surface-treated steel sheet for a battery container,it has been difficult to allow the volume percentage and the corrosionresistance to be compatible with each other when formed into a batterycontainer. In contrast, according to the present embodiment, bycontrolling the thickness of the iron-nickel diffusion layer 12 and theabove-described total amount of the nickel contained in the iron-nickeldiffusion layer 12 and the nickel contained in the nickel layer 14 so asto fall within the above-described ranges, respectively, it is possibleto provide a surface-treated steel sheet 1 being highly balanced betweenthe volume percentage and the corrosion resistance when formed into abattery container.

In addition, there has hitherto been known a method in which thethickness of the iron-nickel diffusion layer is set to be 0.5 μm ormore, in the surface-treated steel sheet having a nickel plating layerand an iron-nickel diffusion layer, for example, from the viewpoint ofimproving the processability when molded as a battery container, fromthe viewpoint of improving the corrosion resistance of the batterycontainer, and from the viewpoint of securing the adhesiveness of theiron-nickel diffusion layer (see, for example, the paragraph 0018 inJapanese Patent Laid-Open No. 2009-263727). Herein, in order to set thethickness of the iron-nickel diffusion layer to be 0.5 μm or more, thecondition of the thermal diffusion treatment after the formation of thenickel plating layer on the steel sheet is required to be a long time ora high temperature. For example, when the condition of the thermaldiffusion treatment is set to be a long time, there have been known theconditions that the heat treatment temperature is set to be 400 to 600°C., and the heat treatment time is set to be 1 to 8 hours. In addition,when the condition of the thermal diffusion treatment is set to be ahigh temperature, there have been known the conditions that the heattreatment temperature is set to be 700 to 800° C., and the heattreatment time is set to be 30 seconds to 2 minutes. Under suchcircumstances, the present inventors have obtained a finding that whenthe thermal diffusion treatment is performed under the above-describedcondition of a long time or a high temperature, the iron of the steelsheet constituting the surface-treated steel sheet is thermally diffusedto an excessive extent, and when the obtained surface-treated steelsheet is molded into a battery container, the amount of iron dissolvedis increased; and accordingly, as described above, the present inventorshave discovered that gas is generated in the interior of the battery,and the internal pressure of the interior of the battery is liable to beincreased due to the generation of the gas. In addition, when thethermal diffusion treatment is performed at a heat treatment temperatureof 700 to 800° C. and at a heat treatment time of 30 seconds to 2minutes, there is a problem that the hardness of the nickel layer 14 isdecreased excessively, and consequently the sticking to the mold occursto a large extent.

In contrast, according to the present embodiment, with respect to thesurface-treated steel sheet 1, by setting the thickness of theiron-nickel diffusion layer 12 to be comparatively as thin as 0.04 to0.31 μm, and by controlling the total amount of the nickel contained inthe iron-nickel diffusion layer and the nickel contained in the nickellayer so as to fall within a range from 10.8 to 26.7 g/m², the exposurearea of the iron of the steel sheet is reduced on the inner surface sidewhen the steel sheet surface-treated steel sheet 1 is molded into abattery container, it is made possible to improve the corrosionresistance when the surface-treated steel sheet 1 is used as a batterycontainer, and in addition, it is made possible to more improve theprocessability when the surface-treated steel sheet 1 is processed intoa battery container.

Such effects as described above are particularly exhibited when there isperformed a processing (such as a processing including ironing) in whichthe thickness is reduced by 10% or more in relation to the originalsheet thickness (the thickness of the surface-treated steel sheet 1).

In addition, in the present embodiment, the thickness of the nickellayer 14 is preferably 1.0 μm or more, more preferably 1.3 μm or more,further preferably 1.5 μm or more, and particularly preferably 1.8 μm ormore. In addition, the upper limit of the thickness of the nickel layer14 is not particularly limited, but is preferably 3.0 μm or less, morepreferably 2.9 μm or less, and further preferably 2.5 μm or less.

Moreover, in the present embodiment, the ratio of the thickness of theiron-nickel diffusion layer 12 to the thickness of the nickel layer 14(thickness of iron-nickel diffusion layer 12/thickness of nickel layer14) is preferably 0.013 to 0.5, more preferably 0.02 to 0.25, furtherpreferably 0.03 to 0.2, and particularly preferably 0.04 to 0.16. Bycontrolling the ratio of (thickness of iron-nickel diffusion layer12/thickness of nickel layer 14) so as to fall within theabove-described range, namely, by controlling the thickness of thenickel layer 14 so as to be comparatively thicker in relation to thethickness of the iron-nickel diffusion layer 12, when thesurface-treated steel sheet 1 is used as a battery container, thecorrosion resistance of the battery container can be further improved.In other words, as described above, with respect to the surface-treatedsteel sheet 1 after the heat treatment, sometimes iron is exposed to theinner surface of the battery container, and local iron exposure portionsappear. In contrast, in the present embodiment, by controlling the ratioof (thickness of iron-nickel diffusion layer 12/thickness of nickellayer 14) so as to fall within the above-described range in such a waythat the thickness of the nickel layer 14 is comparatively thicker inrelation to the thickness of the iron-nickel diffusion layer 12, whenthe surface-treated steel sheet 1 is mold-processed, by using, forexample, a deep drawing processing method, a drawing and ironingprocessing method (DI processing method), a drawing thin and redrawingprocessing method (DTR processing method), or a processing method usinga stretch processing and an ironing processing in combination after adrawing processing, the nickel layer 14 being the outermost layer of thesurface-treated steel sheet 1 is extended due to the stress of the moldprocessing, nickel covers the iron exposed to the surface of thesurface-treated steel sheet 1, and consequently the corrosion resistanceof the obtained battery container can be further improved.

In particular, in the present embodiment, by controlling the thicknessof the nickel layer 14 so as to fall within the above-describedcomparatively thick range of 1.0 μm or more, when the surface-treatedsteel sheet 1 is mold-processed into a battery container, the nickel ofthe nickel layer 14 better covers the iron exposed to the surface of thesurface-treated steel sheet 1, and the corrosion resistance of theobtained battery container is more improved.

The thickness of the nickel layer 14 after the thermal diffusiontreatment can be determined by detecting the boundary between the nickellayer 14 and the iron-nickel diffusion layer 12, on the basis of themeasurement using the above-described high frequency glow dischargeoptical emission spectrometric analyzer. In other words, the time atwhich the measurement of the surface of the surface-treated steel sheet1 is started by using the high frequency glow discharge optical emissionspectrometric analyzer is taken as the starting point, the measurementtime until the time giving the Fe intensity of 10% of the saturatedvalue of the Fe intensity is calculated, and an the basis of thecalculated measurement time, the thickness of the nickel layer 14 can bedetermined. In the present embodiment, the thickness of the iron-nickeldiffusion layer 12 and the thickness of the nickel layer 14 are measuredwith the high frequency glow discharge optical emission spectrometricanalyzer, and by using the obtained measurement results, the ratio of(thickness of iron-nickel diffusion layer 12/thickness of nickel layer14) can be determined.

In addition, in the present embodiment, in the nickel layer 14 after thethermal diffusion treatment, the average crystal grain size in thesurface portion thereof is preferably 0.2 to 0.6 μm, more preferably 0.3to 0.6 μm, and further preferably 0.3 to 0.5 μm. In the presentembodiment, the average crystal grain size in the surface portion of thenickel layer 14 is not particularly limited; when the average crystalgrain size is too small, the plating stress remains accumulated, and inthis case, when mold-processed as a battery container, a deep crackreaching the steel sheet occurs in the surface-treated steel sheet 1,and thus, the iron of the steel sheet 11 is sometimes exposed. In thiscase, iron is dissolved from the exposed portion of the steel sheet 11,and there is an adverse possibility that the gas generated along withthe dissolution of iron increases the internal pressure of the interiorof the battery. On the other hand, as described above, failures occurwhen the cracks reaching the steel sheet 11 are generated in thesurface-treated steel sheet 1; however, from the viewpoint of improvingthe battery properties of the battery container, it is preferable forfine cracks to occur on the inner surface side of the battery containerformed of the surface-treated steel sheet 1. In this regard, when theaverage crystal grain size in the surface portion of the nickel layer 14is too large, the hardness of the nickel layer 14 sometimes comes to betoo low (the nickel layer 14 is softened excessively); in this case,when the surface-treated steel sheet 1 is mold-processed as a batterycontainer, fine cracks cannot be generated on the inner surface of thebattery container, and accordingly, there is an adverse possibility thatthe following effect is not sufficiently obtained: the effect ofimproving the battery properties, namely, the effect of improving thebattery properties by increasing the contact area between the batterycontainer and the positive electrode mixture owing to the cracks andthereby decreasing the internal resistance of the battery.

It is to be noted that the average crystal grain size in the surfaceportion of the nickel layer 14 tends to be larger with the increase ofthe heat treatment temperature in the thermal diffusion treatment, andthe present inventors have discovered that the magnitude of the averagecrystal grain size increases in a stepwise manner depending on thetemperature range. The crystal grains are larger in the case where heattreatment is applied even at a low temperature such as 300° C., ascompared with the case where no heat treatment is applied. When the heattreatment temperature is set to be between 400 and 600° C., the crystalgrain size increases with the increase of the temperature, but thedifference of the magnitude of the crystal grain size due to thetemperature is moderate. When the heat treatment temperature exceeds700° C., the average crystal grain size steeply increases. Accordingly,by controlling the heat treatment temperature of the thermal diffusiontreatment, it is possible to regulate the average crystal grain size inthe surface portion of the nickel layer 14. In particular, bysuppressing the coarsening of the average crystal grain size andallowing the surface hardness of the nickel layer 14 to be hard, it ismade possible to aim at the improvement of the battery properties andthe suppression effect of the sticking of the nickel layer 14 to themold during the processing into the battery container, and accordinglythe heat treatment temperature is particularly preferably 450 to 550° C.In other words, by allowing the surface hardness of the nickel layer 14to be hard by setting the heat treatment temperature so as to fallwithin the above described range, it is made possible to generate finecracks not reaching the steel sheet 11, on the inner surface of thebattery container made of the surface-treated steel sheet 1 when thesurface-treated steel sheet 1 is mold-processed into a batterycontainer, the cracks increases the contact area between the batterycontainer and the positive electrode mixture and decreases the internalresistance of the battery, and thus the battery properties can befurther improved.

In the present embodiment, the average crystal grain size in the surfaceportion of the nickel layer 14 can be determined, for example, by usingthe backscattered electron image obtained by measuring the surface ofthe surface-treated steel sheet 1 with a scanning electron microscope(SEM).

Specifically, first, the surface of the surface-treated steel sheet 1 isetched if necessary, then the surface of the surface-treated steel sheet1 is measured with a scanning electron microscope (SEM), as shown inFIG. 6. It is to be noted that FIG. 6 is an example of the image showingthe backscattered electron image obtained by measuring the actuallyprepared surface-treated steel sheet 1 at a magnification of 10,000.Then, on the obtained backscattered electron image, an optional numberof straight line segments of 10 μm in length are drawn (four lines, forexample). Then, in each of the line segments, on the basis of the numbern of the crystal grains located on the straight line segment, thecrystal grain size d is determined by using the formula d=10/(n+1), andthe average value of the crystal grain sizes d obtained for therespective straight line segments can be taken as the average crystalgrain size in the surface portion of the nickel plating layer 13.

In addition, in the present embodiment, the surface hardness of thenickel layer 14 after the thermal diffusion treatment is a Vickershardness (HV) measured with a load of 10 gf, and the lower limit of theVickers hardness is preferably 220 or more, and more preferably 230 ormore. The upper limit of the Vickers hardness is preferably 280 or less,more preferably 260 or less, and further preferably 250 or less. Bysetting the surface hardness of the nickel layer 14 after the thermaldiffusion treatment so as to fall within the above-described range, theprocessability is improved when the obtained surface-treated steel sheet1 is processed into a battery container, and the corrosion resistance isimproved when the surface-treated steel sheet 1 is used for the batterycontainer. In addition, it is possible to more enhance the suppressioneffect of the sticking to the mold when the surface-treated steel sheet1 is mold processed into a battery container.

In the present embodiment, with respect to the surface-treated steelsheet 1, as a method for controlling the thickness of the iron-nickeldiffusion layer 12 and the total amount of the nickel contained arecontrolled in the iron-nickel diffusion layer and the nickel containedin the nickel layer so as to fall within the above-described ranges,respectively, a method for performing the thermal diffusion treatmentunder the above-described conditions may be mentioned. Specifically,there may be mentioned a method in which after the nickel plating layer13 is formed on the steel sheet 11, a thermal diffusion treatment isperformed under the conditions that the heat treatment temperature is450 to 600° C., and the heat treatment time is 30 seconds to 2 minutes.

In addition, in the present embodiment, with respect to the obtainedsurface-treated steel sheet 1, also as the method for controlling theaverage crystal grain size in the surface portion of the nickel layer 14so as to fall within the above-described range, a method of performing athermal diffusion treatment under the same conditions as described abovemay be mentioned. Specifically, there may be mentioned a method in whichafter the nickel plating layer 13 is formed on the steel sheet 11, athermal diffusion treatment is performed under the conditions that theheat treatment temperature is 450 to 600° C., and the heat treatmenttime is 30 seconds to 2 minutes.

It is to be noted that the thickness of the iron-nickel diffusion layer12 tends to be thick, with the increase of the heat treatmenttemperature, and with the increase of the heat treatment time.Accordingly, by controlling the heat treatment temperature and the heattreatment time of the thermal diffusion treatment, it is possible toregulate the thickness of the iron-nickel diffusion layer 12 and theratio of (thickness of iron-nickel diffusion layer 12/thickness ofnickel layer 14). However, because at a heat treatment temperature of300° C. or lower, it is difficult to form the iron-nickel diffusionlayer, it is preferable to perform the thermal diffusion treatment at480° C. or higher from the viewpoint of controlling the thickness of theiron-nickel diffusion layer 12 and the ratio of (thickness ofiron-nickel diffusion layer 12/thickness of nickel layer 14) so as tofall within the above-described ranges.

The surface-treated steel sheet 1 of the present embodiment isconstituted as described above.

The surface-treated steel sheet 1 of the present embodiment is used asmold-processed into the positive electrode can 21 of an alkaline battery2 shown in FIGS. 1 and 2, battery containers of other batteries and thelike, by using, for example, a deep drawing processing method, a drawingand ironing processing method (DI processing method), a drawing thin andredrawing processing method (DTR processing method), or a processingmethod using a stretch processing and an ironing processing incombination after a drawing processing.

<Method for Producing Surface-Treated Steel Sheet 1>

Next, a method for producing the surface-treated steel sheet 1 of thepresent embodiment is described.

First, the steel sheet 11 is prepared, and as described above, a nickelplating is applied to the steel sheet 11, to form the nickel platinglayer 13 on the surface of the steel sheet 11, to be the inner surfaceof a battery container. It is to be noted that the nickel plating layer13 is preferably formed not only on the surface of the steel sheet 11 tobe the inner surface of the battery container but also on the oppositesurface. When the nickel plating layer 13 is formed on both surfaces ofthe steel sheet 11, the nickel plating layers 13 different from eachother in the composition and the surface roughness may be formed on thesurface in the steel sheet 11 to be the inner surface of the batterycontainer and on the surface of the steel sheet 11 to be the outersurface of the battery container, respectively, by using plating bathshaving different compositions; however, from the viewpoint of improvingthe production efficiency, it is preferable to form the nickel platinglayers 13 on both surfaces of the steel sheet 11, by using the sameplating bath in one step.

Next, by performing the thermal diffusion treatment under theabove-described conditions for the steel sheet 11 having the nickelplating layer 13 formed thereon, the iron constituting the steel sheet11 and the nickel constituting the nickel plating layer 13 are allowedto thermally diffuse, to from the iron-nickel diffusion layer 12 and thenickel layer 14. Herewith, the surface-treated steel sheet 1 as shown inFIG. 3 is obtained.

It is to be noted that in the present embodiment, a temper rolling maybe applied to the obtained surface-treated steel sheet 1. Herewith, itis possible to regulate the surface roughness of the surface of thesurface-treated steel sheet 1 to be the inner surface of the batterycontainer; when the surface-treated steel sheet 1 is used as a batterycontainer, the contact area between the battery container and thepositive electrode mixture can be increased, the internal resistance ofthe battery can be decreased, and the battery properties can beimproved.

As described above, the surface-treated steel sheet 1 of the presentembodiment is produced.

In the surface-treated steel sheet 1 of the present embodiment, asdescribed above, by setting the thickness of the iron-nickel diffusionlayer 12 to be comparatively as thin as 0.04 to 0.31 μm, and bycontrolling the total amount of the nickel contained in the iron-nickeldiffusion layer and the nickel contained in the nickel layer so as tofall within a range from 10.8 to 26.7 g/m², it is possible toeffectively prevent the generation of gas even when the alkaline battery2 prepared by using the surface-treated steel sheet 1 is used or storedover a long term, and herewith it is possible to prevent the increase ofthe internal pressure of the interior of the battery due to thegeneration of gas. Moreover, as described above, by setting thethickness of the nickel layer 14 to be preferably 1.0 μm or more, thecorrosion resistance is more improved when the surface-treated steelsheet 1 is used for the battery container, and it is possible to moreeffectively prevent the gas generation in such an interior of a batteryand the increase of the internal pressure due to the gas generation.Accordingly, the surface-treated steel sheet 1 of the present embodimentcan be suitably used as the battery containers of the batteries such asalkaline batteries, the batteries using alkaline electrolytic solutionssuch as nickel-hydrogen batteries, and lithium-ion batteries.

EXAMPLES

Hereinafter, the present invention is described more specifically withreference to Examples, but the present invention is not limited to theseExamples.

Example 1

As a base sheet, there was prepared a steel sheet 11 obtained byannealing a cold rolled sheet (thickness: 0.25 am) of a low-carbonaluminum-killed steel having the chemical composition shown below:

C: 0.045% by weight, Mn: 0.23% by weight, Si: 0.02% by weight, P: 0.012%by weight, S: 0.009% by weight, Al: 0.063% by weight, N: 0.0036% byweight, the balance: Fe and inevitable impurities.

Then, the prepared steel sheet 11 was subjected to alkaline electrolyticdegreasing and sulfuric acid immersion pickling, then subjected toelectrolytic plating under the below-described conditions, and thus anickel plating layer 3 was formed on the steel sheet 11 so as to have aplating deposition amount of 17.8 g/m². Subsequently, as for thethickness of the nickel plating layer 13, the deposition amount thereofwas determined by performing a fluorescent X-ray measurement. Theresults thus obtained are shown in Table 1.

Bath composition: nickel sulfate: 250 g/L, nickel chloride: 45 g/L,boric acid: 45 g/L

pH: 3.5 to 4.5

Bath temperature: 60° C.

Electric current density: 20 A/dm²

Energizing time: 32 seconds

Next, the steel sheet 11 having the nickel plating layer 13 formedthereon was subjected to a thermal diffusion treatment by continuousannealing under the conditions of a heat treatment temperature of 480°C., a heat treatment time of 30 seconds, and a reductive atmosphere, andthus an iron-nickel diffusion layer 12 and a nickel layer 14 wereformed, to obtain a surface-treated steel sheet 1.

Next, the obtained surface-treated steel sheet 1 was subjected to atemper rolling under the condition of an extension percentage of 1%.

Then, by using the surface-treated steel sheet 1 after the temperrolling, according to the below-described methods, the measurement ofthe thickness of the iron-nickel diffusion layer 12 and the thickness ofthe nickel layer 14 was performed.

<Measurement of Thickness of Iron-Nickel Diffusion Layer 12 andThickness of Nickel Layer 14>

With respect to the surface-treated steel sheet 1, by using a highfrequency glow discharge optical emission spectrometric analyzer, thevariations of the Fe intensity and the Ni intensity were continuouslymeasured in the depth direction from the outermost layer toward thesteel sheet 11, the time giving the Fe intensity of 10% of the saturatedvalue of the Fe intensity is taken as the starting point, themeasurement time until the time giving the Ni intensity an intensity of10% of the maximum value of the Ni intensity after the Ni intensity hadexhibited the maximum value thereof was calculated, and on the basis ofthe calculated measurement time, the thickness of the iron-nickeldiffusion layer 12 was determined. It is to be noted that when thethickness of the iron-nickel diffusion layer 12 was determined, thethickness of the iron-nickel diffusion layer 12 was measured, first, onthe basis of the results obtained by performing the high frequency glowdischarge optical emission spectrometric analysis of the below-describednickel-plated steel sheet (Comparative Example 2) undergoing no thermaldiffusion treatment, the measurements were performed by taking as thereference thickness the thickness measured as the iron-nickel diffusionlayer (the value obtained by converting the measurement time into thethickness as follows: the time giving the Fe intensity 10% of thesaturated value of the Fe intensity was taken as the starting point, themeasurement time until the time giving the Ni intensity 10% of themaximum value after the Ni intensity had exhibited the maximum valuethereof was converted into the thickness). It is to be noted that thereference thickness was 0.17 μm. In addition, the thickness of theactual iron-nickel diffusion layer 12 in Example 1 was determined bysubtracting the reference thickness from the thickness of theiron-nickel diffusion layer 12 portion (the value obtained by convertingthe measurement time into the thickness as follows: the time giving theFe intensity 10% of the saturated value of the Fe intensity was taken asthe starting point, and the measurement time until the time giving theNi intensity 10% of the maximum value after the Ni intensity hadexhibited the maximum value thereof was converted into the thickness) ofthe surface-treated steel sheet 1 of Example 1. In addition, for thenickel layer 14, by taking as the starting point the time at which themeasurement of the surface of the surface-treated steel sheet 1 wasstarted with the high frequency glow discharge optical emissionspectrometric analyzer, the measurement time until the Fe intensity wasgiven an intensity of 10% of the saturated value of the Fe intensity wascalculated, and on the basis of the calculated measurement time, thethickness of the nickel layer 14 was determined. Then, on the basis ofthe measurement result, the ratio of the thickness of the iron-nickeldiffusion layer 12 to the thickness of the nickel layer 14 (thickness ofiron-nickel diffusion layer 12/thickness of nickel layer 14) wasdetermined. The results thus obtained are shown in Table 1. It is to benoted that, in Table 1, the ratio of (thickness of iron-nickel diffusionlayer 12/thickness of nickel layer 14) was described as “Thickness ratioFe—Ni/Ni.”

It is to be noted that in the measurement with a high frequency glowdischarge optical emission spectrometric analyzer, with the increase ofthe thickness of the nickel plating layer, the reference thicknesscalculated from the measurement of the nickel plating layer comes to beincreased; thus, when the thickness of the iron-nickel diffusion layeris determined, the reference thickness is checked in the platingdeposition amount of each of the layers, or alternatively, it isdesirable that the measurement of the reference thickness is performedin each of the two or more samples, different from each other in theplating deposition amount before performing heat treatment, the relationformula between the plating deposition amount and the referencethickness is determined, and then the thickness of the iron-nickeldiffusion layer is calculated

Examples 3 to 6, 8 to 11, and 13 to 19 and Reference Examples 2 to 4

In each of Examples 3 to 6, 8 to 11, and 13 to 19 and Reference Examples2 to 4, a surface-treated steel sheet 1 was obtained in the same manneras in Example 1 except that the plating deposition amount of the nickelplating layer 13, and the continuous annealing conditions (heattreatment conditions) for the steel sheet 11 having a nickel plating 13formed thereon were altered as shown in Table 1, and the measurementswere performed in the same manner. The results thus obtained are shownin Table 1. It is to be noted that in Examples 3 and 6 and ReferenceExamples 2 to 4, the reference thickness used in the calculation of thethickness of the iron-nickel diffusion layer was calculated by derivingthe relation formula between the plating deposition amount and thereference thickness from the reference thickness values calculated frombelow-described Comparative Example 1 and Comparative Example 2.

Comparative Example 1

A nickel-plated steel sheet was prepared under the same conditions as inExample 1 except that the plating deposition amount of the nickelplating layer 13 was altered from 17.8 g/m² to 8.0 g/m², and neither acontinuous annealing nor a temper rolling was performed after the nickelplating layer 13 was formed. In the prepared nickel-plated steel sheet,the thickness of the nickel plating layer 13 was determined as thethickness of the nickel layer 14. The results thus obtained are shown inTable 1.

Comparative Example 2

A nickel-plated steel sheet was prepared under the same conditions as inExample 1 except that neither a continuous annealing nor a temperrolling was performed after the nickel plating layer 13 was formed. Inthe prepared nickel-plated steel sheet, the thickness of the nickelplating layer 13 was determined as the thickness of the nickel layer 14.The results thus obtained are shown in Table 1.

Comparative Examples 3 to 10

In each of Comparative Examples 3 to 10, a surface-treated steel sheet 1was obtained in the same manner as in Example 1 except that the platingdeposition amount of the nickel plating layer 13, and the continuousannealing conditions (heat treatment conditions) for the steel sheet 11having a nickel plating layer 13 formed thereon were altered as shown inTable 1, and the measurements were performed in the same manner. Theresults thus obtained are shown in Table 1. It is to be noted that inComparative Example 3, the thickness of the iron-nickel diffusion layer12 was equal to or smaller than the detection limit value (0.04 μm) ofthe high frequency glow discharge optical emission spectrometricanalyzer, and accordingly the thickness of the iron-nickel diffusionlayer 12 was regarded to be more than 0 μm and less than 0.04 μm, andthe “thickness ratio Fe—Ni/Ni” was taken to be “0<”.

Reference Example 1

A nickel-plated steel sheet was prepared under the same conditions as inExample 1 except that the plating deposition amount of the nickelplating layer 13 was altered from 18.2 g/m² to 10.6 g/m², and neither acontinuous annealing nor a temper rolling was performed after the nickelplating layer 13 was formed. Then, the prepared nickel-plated steelsheet was subjected to measurements, as described above, on the basis ofthe high frequency glow discharge optical emission spectrometricanalysis to obtain the measurement results shown in FIG. 5(B), and themeasurements were performed by taking as the reference thickness thethickness measured as the iron-nickel diffusion layer (the valueobtained by converting the measurement time into the thickness asfollows: in FIG. 5(B), the time giving the Fe intensity 10% of thesaturated value of the Fe intensity was taken as the starting point, themeasurement time until the time giving the Ni intensity 10% of themaximum value after the Ni intensity had exhibited the maximum valuethereof was converted into the thickness). The results thus obtained areshown in Table 1 and FIG. 5(B).

Example 20

The prepared steel sheet 11 was subjected to alkaline electrolyticdegreasing and sulfuric acid immersion pickling, and then subjected toelectrolytic plating under the below-described conditions, in a platingbath prepared by adding, to the below-described base composition bath, asemi-gloss agent containing 0.16 ml/L of an aliphatic unsaturatedalcohol, 0.38 ml/L of an unsaturated carboxylic acid, 0.3 ml/L offormaldehyde and 0.064 ml/L of methanol; thus a nickel plating layer 13was formed an the steel sheet 11 so as to have a plating depositionamount of 17.8 g/m². Subsequently, as for the thickness of the nickelplating layer 13, the deposition amount thereof was determined byperforming a fluorescent X-ray measurement.

Bath composition: Nickel sulfate: 250 g/L, nickel chloride: 45 g/L,boric acid: 45 g/L

pH: 3.5 to 4.5

Bath temperature: 60° C.

Electric current density: 20 A/dm²

Energizing time: 32 seconds

Next, the steel sheet 11 having the nickel plating layer 13 formedthereon was subjected to a thermal diffusion treatment by continuousannealing under the conditions of a heat treatment temperature of 450°C., a heat treatment time of 30 seconds, and a reductive atmosphere, andthus an iron-nickel diffusion layer 12 and a nickel layer 14 wereformed, to obtain a surface-treated steel sheet 1.

Next, the obtained surface-treated steel sheet 1 was subjected to atemper rolling under the condition of an extension percentage of 1%.

Then, the measurement of the thickness of the iron-nickel diffusionlayer 12 and the thickness of the nickel layer 14 was performed by usingthe surface-treated steel sheet 1 after the temper rolling, according tothe below-described method.

Examples 21 to 26

In each of Examples 21 to 26, a surface-treated steel sheet 1 wasobtained in the same manner as in Example 20 except that the continuousannealing conditions (heat treatment conditions) for the steel sheet 11having a nickel plating layer 13 formed thereon were altered as shown inTable 1, and the measurements were performed in the same manner. Theresults thus obtained are shown in Table 1.

Comparative Example 11

The prepared steel sheet 11 was subjected to alkaline electrolyticdegreasing and sulfuric acid immersion pickling, and then subjected toelectrolytic plating under the below-described conditions, in a platingbath prepared by adding, to the below-described base composition bath, asemi-gloss agent containing 0.16 ml/L of an aliphatic unsaturatedalcohol, 0.38 ml/L of an unsaturated carboxylic acid, 0.3 ml/L offormaldehyde and 0.064 ml/L of methanol; thus a nickel plating layer 13was formed on the steel sheet 11 so as to have a plating depositionamount of 17.8 g/m². Subsequently, as for the thickness of the nickelplating layer 13, the deposition amount thereof was determined byperforming a fluorescent X-ray measurement.

Bath composition: Nickel sulfate: 250 g/L, nickel chloride: 45 g/L,boric acid: 45 g/L

pH: 3.5 to 4.5

Bath temperature: 60° C.

Electric current density: 20 A/dm²

Energizing time: 32 seconds

Next, the steel sheet 11 having the nickel plating layer 13 formedthereon was subjected to a thermal diffusion treatment by continuousannealing under the conditions of a heat treatment temperature of 650°C., a heat treatment time of 30 seconds, and a reductive atmosphere, andthus an iron-nickel diffusion layer 12 and a nickel layer 14 wereformed, to obtain a surface-treated steel sheet 1.

Next, the obtained surface-treated steel sheet 1 was subjected to atemper rolling under the condition of an extension percentage of 1%.

Then, the measurement of the thickness of the iron-nickel diffusionlayer 12 and the thickness of the nickel layer 14 was performed by usingthe surface-treated steel sheet 1 after the temper rolling, according tothe below-described method.

Comparative Example 12

A surface-treated steel sheet 1 was obtained in the same manner as inExample 20 except that the continuous annealing conditions (heattreatment conditions) for the steel sheet 11 having a nickel platinglayer 13 formed thereon were altered as shown in Table 1, and themeasurements were performed in the same manner. The results thusobtained are shown in Table 1.

Comparative Example 13

A nickel-plated steel sheet was prepared under the same conditions as inComparative Example 12 except that neither a continuous annealing nor atemper rolling was performed after the nickel plating layer 13 wasformed. In the prepared nickel-plated steel sheet, the thickness of thenickel plating layer 13 was determined as the thickness of the nickellayer 14. The results thus obtained are shown in Table 1.

TABLE 1 Before heat treatment Heat treatment After heat treatmentPlating conditions Nickel layer 14 Iron-nickel Thickness amountTemperature Thickness diffusion layer 12 ratio (g/m²) [° C.] Time [μm]Thickness [μm] Fe—Ni/Ni Remark Example 1 18.2 480 30 sec 2.00 0.10 0.050Example 2 29.3 480 30 sec 3.23 0.12 0.038 Example 3 12.2 500 30 sec 1.320.11 0.083 Example 4 19.2 500 30 sec 2.10 0.13 0.06 Example 5 18.6 50030 sec 2.01 0.15 0.075 Example 6 23.8 500 30 sec 2.63 0.09 0.034 Example7 29.1 500 30 sec 3.20 0.12 0.038 Example 8 19.2 550 30 sec 2.08 0.150.072 Example 9 17.8 580 30 sec 1.89 0.21 0.111 Example 10 20.0 600 30sec 2.12 0.25 0.12 Example 11 18.8 600 30 sec 1.98 0.27 0.136 Example 1230.5 600 30 sec 3.33 0.19 0.056 Example 13 18.2 480 30 sec 2.00 0.100.052 Example 14 17.7 480 60 sec 1.94 0.10 0.050 Example 15 17.9 500 60sec 1.92 0.18 0.093 Example 16 19.2 550 60 sec 2.08 0.15 0.07 Example 1717.5 580 30 sec 1.89 0.15 0.080 Example 18 17.4 580 60 sec 1.86 0.180.096 Example 19 17.9 600 60 sec 1.98 0.27 0.140 Comparative 9.0 — —1.00 none — Example 1 Comparative 18.0 — — 2.00 none — Example 2Comparative 18.1 350 30 sec 2.01 More than 0 μm, 0< Example 3 less than0.04 μm Comparative 9.7 500 60 min 0.91 0.35 0.39 Example 4 Comparative17.2 500 60 min 1.77 0.33 0.186 Example 5 Comparative 9.9 700 30 sec0.89 0.44 0.494 Example 6 Comparative 18.6 700 30 sec 1.87 0.45 0.241Example 7 Comparative 18.0 400 60 sec 2.06 More than 0 μm, 0< Example 8less than 0.04 μm Comparative 19.1 450 360 min 1.62 1.05 0.651 Example 9Comparative 19.5 500 360 min 1.65 1.08 0.658 Example 10 Reference 10.6 —— Reference Reference — Example 1 thickness thickness Example 20 18.0450 30 sec 1.74 0.22 0.127 Semi-gloss Example 21 18.2 480 30 sec 1.760.23 0.133 Semi-gloss Example 22 17.7 500 30 sec 1.70 0.23 0.138Semi-gloss Example 23 18.1 500 60 sec 1.73 0.26 0.15 Semi-gloss Example24 17.8 550 30 sec 1.70 0.26 0.153 Semi-gloss Example 25 18.4 550 60 sec1.76 0.27 0.152 Semi-gloss Example 26 18.5 580 30 sec 1.76 0.31 0.173Semi-gloss Comparative 17.9 650 30 sec 1.68 0.33 0.197 Semi-glossExample 11 Comparative 18.8 700 30 sec 1.74 0.41 0.235 Semi-glossExample 12 Comparative 18.0 — — — Semi-gloss Example 13

Next, the surface-treated steel sheets 1 of Examples 3, 5, 6, 8, 11, 13to 19 and 22 and Comparative Examples 4 to 10, and the nickel-platedsteel sheet of Comparative Examples 1 and 2 were evaluated according tothe below-described method, with respect to the corrosion resistancewhen each of these steel sheets was molded into a battery container.

<Evaluation of Corrosion Resistance>

A blank was prepared by punching out a surface-treated steel sheet 1into a predetermined shape with a press machine, the obtained blank wassubjected to a drawing and ironing processing in such a way that thenickel layer 14 was on the inner surface side, and thus a batterycontainer was prepared (it is to be noted that when a nickel-platedsteel sheet was used, a battery container was prepared in such a waythat the nickel plating layer 13 was on the inner surface side).Specifically, a tubular body was obtained by applying a drawing andironing processing to the blank by using a drawing and ironing machineincluding drawing dies or ironing dies, each having a predeterminedclearance, arranged in six stages and a punch, and a battery containerwas obtained by cutting the lug part in the vicinity of the opening ofthe obtained tubular body. The drawing and ironing processing used thedies in each of which the clearance was set in such a way that thethickness of the can bottom at a position of 10 mm from the can bottomafter processing was 0.15 mm.

Next, the obtained battery container was evaluated with respect to theamount of Fe ions dissolved as follows: the obtained battery containerwas filled with a 10 mol/L potassium hydroxide solution, sealed andstored under the conditions of 60° C., 480 hours, then the amount of Feions dissolved from the inner surface of the battery container into thesolution was measured with a high frequency inductively coupled plasmaemission spectrometric analyzer (ICP) (ICPE-9000, manufactured byShimadzu Corp.), and the amount of Fe ions dissolved was evaluated onthe basis of the following standards. When the evaluation was A+, A, Bor C in the following standards, the dissolution of iron from the innersurface of the battery container was determined to be sufficientlysuppressed. The results thus obtained are shown in Table 2.

A+: The amount of Fe ions dissolved was less than 30 mg/L.

A: The amount of Fe ions dissolved was 30 mg/L or more and less than 33mg/L.

B: The amount of Fe ions dissolved was 33 mg/L or more and less than 36mg/L.

C: The amount of Fe ions dissolved was 36 mg/L or more and less than 37mg/L.

D: The amount of Fe ions dissolved was 38 mg/L or more.

D−: The amount of Fe ions dissolved was 40 mg/L or more.

TABLE 2 Before heat treatment Heat treatment After heat treatmentPlating conditions Nickel layer 14 Iron-nickel Thickness amountTemperature Thickness diffusion layer 12 ratio Corrosion (g/m²) [° C.]Time [μm] Thickness [μm] Fe—Ni/Ni resistance Remark Example 3 12.2 50030 sec 1.32 0.11 0.083 A Example 5 18.6 500 30 sec 2.01 0.15 0.075   A+Example 6 23.8 500 30 sec 2.63 0.09 0.034   A+ Example 8 19.2 550 30 sec2.08 0.15 0.072   A+ Example 11 18.8 600 30 sec 1.98 0.27 0.136 AExample 13 18.2 480 30 sec 2.00 0.10 0.052 A Example 14 17.7 480 60 sec1.94 0.10 0.050 A Example 15 17.9 500 60 sec 1.92 0.18 0.093   A+Example 16 19.2 550 60 sec 2.08 0.15 0.07 A Example 17 17.5 580 30 sec1.89 0.15 0.080 B Example 18 17.4 580 60 sec 1,86 0.18 0.096 B Example19 17.9 600 60 sec 1.98 0.27 0.140 C Example 22 17.7 500 30 sec 1.700.23 0.138   A+ Semi-gloss Comparative 9.0 — — 1.00 none —   D− Example1 Comparative 18.0 — — 2.00 none —   D− Example 2 Comparative 9.7 500 60min 0.91 0.35 0.39   D− Example 4 Comparative 17.2 500 60 min 1.77 0.330.186 D Example 5 Comparative 9.9 700 30 sec 0.89 0.44 0.494 D Example 6Comparative 18.6 700 30 sec 1.87 0.45 0.241 D Example 7 Comparative 18.0400 60 sec 2.06 0※ 0※ D Example 8 Comparative 19.1 450 360 min 1.62 1.050.651   D− Example 9 Comparative 19.5 500 360 min 1.65 1.08 0.658   D−Example 10

As shown in Table 2, Examples 3, 5, 6, 8, 11, 13 to 19, and 22 in eachof which the thickness of the iron-nickel diffusion layer 12 was 0.04 to0.31 Nm, and the total amount of the nickel contained in the iron-nickeldiffusion layer and the nickel contained in the nickel layer was 10.8 to26.7 g/m² (the thickness of the nickel plating layer 13 was 1.21 to 3.0μm) gave the results that these Examples were all excellent in corrosionresistance.

On the other hand, as shown in Table 2, Comparative Examples 1 and 2free from the application of a thermal diffusion treatment gave theresults that these Comparative Examples were poor in corrosionresistance; moreover, it is conceivable that the iron-nickel diffusionlayer 12 was not formed due to the omission of the thermal diffusiontreatment, and accordingly these Comparative Examples were poor in theadhesiveness between the steel sheet 11 and the nickel plating layer 13.

In addition, even in the case where the thermal diffusion treatment wasperformed, when the total amount of the nickel contained in theiron-nickel diffusion layer and the nickel contained in the nickel layerwas too small (the thickness of the nickel plating layer 13 was toothin), the improvement effect of the corrosion resistance due to nickelwas insufficient, and the result that the corrosion resistance was poorwas obtained as in Comparative Examples 4 and 6. Also, in the case wherethe thickness of the iron-nickel diffusion layer 12 was too thin, theresult that the corrosion resistance was poor was obtained as inComparative Example 8.

Moreover, even in the case where the thermal diffusion treatment wasperformed, when the thickness of the iron-nickel diffusion layer 12 wasmade too thick due to an excessive thermal diffusion treatment, iron wasprobably exposed to the surface of the nickel layer 14, and the resultthat the corrosion resistance was poor was obtained as in ComparativeExamples 4 to 7, 9, and 10.

Next, there was performed a measurement of the surface hardness of eachof the surface-treated steel sheets 1 of Examples 1, 5, 8, 9, 11, 20,and 22, Reference Example 4, and Comparative Examples 6 and 7, and thenickel-plated steel sheets of Comparative Examples 1, 2, and 13,according to the below-described method.

<Measurement of Surface Hardness>

For the nickel layer 14 of the surface-treated steel sheet 1 (or thenickel plating layer 13 of the nickel-plated steel sheet), the surfacehardness measurement was performed by measuring the Vickers hardness(HV) with a micro hardness tester (model: MVK-G2, manufactured by AkashiSeisakusho Co., Ltd.), by using a diamond indenter, under the conditionsof a load of 10 gf and a holding time of 10 seconds, and the resultobtained was evaluated on the basis of the following standards. When theevaluation was A or B in the following standards, it was determined thatthe hardness was within an appropriate range, the processability whenthe surface-treated steel sheet 1 was processed into a battery container(the capability of generating fine cracks to an appropriate extent onthe inner surface of the battery container when mold-processed into abattery container) and the suppression effect of the sticking to themold were excellent, and additionally, the corrosion resistance whenused for the battery container was excellent. The results obtained areshown in Table 3.

A: 230 or more and less than 280

B: 220 or more and less than 230

C: 280 or more

D: less than 220.

TABLE 3 Before heat treatment Heat treatment After heat treatmentSurface hardness Plating conditions Nickel layer 14 Iron-nickelThickness Vickers amount Temperature Thickness diffusion layer 12 ratiohardness (g/m²) [° C.] Time [μm] Thickness [μm] Fe—Ni/Ni (HV) EvaluationRemark Example 1 18.2 480 30 sec 2.00 0.10 0.050 248 A Example 5 18.6500 30 sec 2.01 0.15 0.075 241 A Example 8 19 2 550 30 sec 2.08 0.150.072 231 A Example 9 17.8 580 30 sec 1.89 0.21 0.111 224 B Example 1118.8 600 30 sec 1.98 0.27 0.136 220 B Example 12 30.5 600 30 sec 3.330.19 0.056 220 B Example 20 18.0 450 30 sec 1.74 0.22 0.127 270 ASemi-gloss Example 22 17.7 500 30 sec 1.70 0.23 0.138 245 A Semi-glossComparative 9.0 — — 1.00 none — 289 C Example 1 Comparative 18.0 — —2.00 none — 315 C Example 2 Comparative 9.9 700 30 sec 0.89 0.44 0.494209 D Example 6 Comparative 18.6 700 30 sec 1.87 0.45 0.241 217 DExample 7 Comparative 18.0 — — — 415 C Semi-gloss Example 13

As shown in Table 3, Examples 1, 5, 8, 9, 11, 20, and 22 in each ofwhich the thickness of the iron-nickel diffusion layer 12 was 0.04 to0.31 μm, and the total amount of the nickel contained in the iron-nickeldiffusion layer and the nickel contained in the nickel layer was 10.8 to26.7 g/m² (the thickness of the nickel plating layer 13 was 1.21 to 3.0μm) gave the results that the hardness of any of these Examples fellwithin an appropriate range, and herewith, it is conceivable that any ofthese Examples was excellent in the processability and the suppressioneffect of the sticking to the mold when the surface-treated steel sheet1 was processed into a battery container, and moreover excellent in thecorrosion resistance when the surface-treated steel sheet 1 was used forthe battery container.

On the other hand, as shown in Table 3, each of Comparative Examples 1,2, and 13 free from the application of the thermal diffusion treatmentunderwent a too high hardness, and herewith there was an adversepossibility that when the surface treated steel sheet 1 wasmold-processed into a battery container, deep cracks reaching the steelsheet 11 were generated, the iron of the steel sheet 11 was exposed, andthe corrosion resistance was decreased.

Alternatively, even in the case where the thermal diffusion treatmentwas performed, when the total amount of the nickel contained in theiron-nickel diffusion layer and the nickel contained in the nickel layerwas too small (the thickness of the nickel plating layer 13 was toothin), the hardness came to be too low as in Comparative Example 6, andherewith it is conceivable that the processability and the suppressioneffect of the sticking to the mold when the surface-treated steel sheetwas processed into a battery container were poor.

Moreover, even in the case where the thermal diffusion treatment wasperformed, when the thickness of the iron-nickel diffusion layer 12 cameto be too thick due to an excessive thermal diffusion treatment, thehardness was too low as in Comparative Examples 6 and 7, and herewith itis conceivable that the processability and the suppression effect of thesticking to the mold when the surface-treated steel sheet was processedinto a battery container were poor.

REFERENCE SIGNS LIST

-   1 . . . surface-treated steel sheet    -   11 . . . steel sheet    -   12 . . . iron-nickel diffusion layer    -   13 . . . nickel plating layer    -   14 . . . nickel layer-   2 . . . alkaline battery    -   21 . . . positive electrode can        -   211 . . . positive electrode terminal    -   22 . . . negative electrode terminal    -   23 . . . positive electrode mixture    -   24 . . . negative electrode mixture    -   25 . . . separator    -   26 . . . current collector    -   27 . . . gasket    -   28 . . . insulating ring    -   29 . . . exterior case

The invention claimed is:
 1. A battery container, comprising: a bottomedcylindrical shaped article made of a surface-treated steel sheet,wherein the surface-treated steel sheet comprises: a steel sheet; aniron-nickel diffusion layer formed on the steel sheet; and a nickellayer formed on the iron-nickel diffusion layer and constituting theoutermost layer, the nickel layer consisting of nickel, wherein when theFe intensity and the Ni intensity are continuously measured from thesurface of the surface-treated steel sheet for a battery container alongthe depth direction with a high frequency glow discharge opticalemission spectrometric analyzer, the thickness of the iron-nickeldiffusion layer being the difference (D2−D1) between the depth (D1) atwhich the Fe intensity exhibits a first predetermined value and thedepth (D2) at which the Ni intensity exhibits a second predeterminedvalue is 0.04 to 0.31 μm, wherein the total amount of the nickelcontained in the iron-nickel diffusion layer and the nickel contained inthe nickel layer is 10.8 to 26.7 g/m², wherein the depth (D1) exhibitingthe first predetermined value is the depth exhibiting an intensity of10% of the saturated value of the Fe intensity measured by theabove-described measurement, wherein the depth (D2) exhibiting thesecond predetermined value is the depth exhibiting an intensity of 10%of the maximum value when the measurement is further performed along thedepth direction after the Ni intensity shows the maximum value by theabove-described measurement, and wherein the iron-nickel diffusion layeris disposed on an inner surface of the bottomed cylindrical shapedarticle.
 2. The battery container according to claim 1, wherein theratio of the thickness of the iron-nickel diffusion layer to thethickness of the nickel layer (thickness of iron-nickel diffusionlayer/thickness of nickel layer) is 0.013 to 0.50.
 3. The batterycontainer according to claim 1, wherein the thickness of the nickellayer is 1.0 μm or more.
 4. The battery container according to claim 1,wherein the Vickers hardness (HV) of the nickel layer measured with aload of 10 gf is 220 to
 280. 5. A battery provided with the batterycontainer according to claim
 1. 6. The battery container according toclaim 1, wherein the bottomed cylindrical shaped article is a batterycan.
 7. The battery container according to claim 1, wherein the bottomedcylindrical shaped article is a positive electrode can.
 8. A method forproducing a battery container having a surface-treated steel sheet, saidmethod comprising: forming a bottomed cylindrical shaped article havingan inner surface; and forming the surface-treated steel sheet by amethod comprising: forming a nickel plating layer on a surface of asteel sheet with a nickel amount of 10.8 to 26.7 g/m²; and forming aniron-nickel diffusion layer and a nickel layer constituting an outermostlayer by applying a heat treatment to the steel sheet having the nickelplating layer formed thereon by maintaining the steel sheet at atemperature of 450 to 600° C. for 30 seconds to 2 minutes, wherein thenickel plating layer is formed on the inner surface of the bottomedcylindrical shaped article and consists of nickel.